You need to put Premise Builder into Expert Mode. In that mode, there's no Wizard and you get complete freedom to create most anything (and complete freedom to screw things up; no safety net other than a backup copy of your Premise Home).

In Premise Builder, click Modules, click your Module, then click on anything listed in the center of the screen (your cursor needs to be there for this next part to work).

Now press Ctrl+Shift+A

A message will appear warning you are now entering Expert Mode.

Right-click one of the classes in your Module and you'll see new options including to the ability to create new Properties, different kinds of Scripts (OnChangeProperty which only runs when a property changes state, or Constructor which only runs the first time your class is instantiated as an object, etc) plus Relationships (make your new class Inherit from another class, make your new class Extend another class, or make your class an Object Container).

Credit where credit is due, I learned about Expert Mode from Jim Springer. I couldn't figure out how to bind to an X10 HR12a keypad ... it simply wasn't seen as a 'bindable' keypad. Jim's instructions showed how to make it inherit from another class (KeypadDevice) and the process required Expert Mode.

It's all here, posted .... a decade ago! Geez, where does the time go?!?

Really close.
I have this property:Receiver/AudioVideoSwitch/CurrentSource

Which lets me navigate here:Schema > Device > AudioVideo > Reciever
Where it offers 2 un-labeled folders (they show up as DefaultSources and OptionalSources when you select them). In those folders are the inputs the receiver offers. I want to add a Blu-Ray player option there......

I'm also assuming that it will cascade down to the custom receiver driver I am writing, because that object inherits the Receiver_Device class

This is the kind of behavior I can't explain because I don't know how the underlying code works (i.e. it is not shown anywhere). Sorry, this question will have to be fielded by someone with a deeper understanding of MediaZones and AudioVideo devices.